Optically-active D-amino acids are important compounds as intermediate compounds for drugs and it has been known that they can be produced efficiently by combining an asymmetric hydrolysis reaction of 5-substituted hydantoins into the corresponding D-N-carbamyl-.alpha.-amino acids with the enzymes, hydantoinases (hereinafter sometimes abbreviated as "Hase") (JP-B 62-30785), and an conversion reaction of the resultant D-N-carbamyl-a-amino acids into the corresponding D-.alpha.-amino acids with the enzymes, D-N-carbamyl-.alpha.-amino acid .alpha.-midohydrolases (hereinafter sometimes abbreviated as "decarbamylase" or "DCase") (PCT/JP91/01696: WO 92/10579).
In addition, JP-A 63-185382, WO 92/00739 and the like disclose that the respective reactions are carried out more efficiently by using these enzymes in the form of so- called immobilized enzymes wherein they are immobilized on supports such as ion exchange resins and the like.
However, a two-step reaction has been employed for carrying out these reactions because the optimal and stable pH's of both enzymes are considerably different from each other. Therefore, both immobilized enzymes should be prepared separately and complicated reaction operations are required.